Iron is an essential micronutrient for bacterial pathogens and their mammalian hosts, and hence competition for this element is an integral component of the infectious process. Extracellular ferrous iron is biologically unavailable to invading pathogens because it is largely sequestered to host proteins, and in its free form rapidly oxidizes to the insoluble ferric state. Bacteria often respond to the iron withholding system of the host by turning on iron scavenging systems and virulence determinants to promote bacterial survival and dissemination. Among the most extensively studied metal ion-dependent regulators in Gram-positive bacteria is DtxR, a DNA-binding protein, in Corynebacterium diphtheriae, and its phylogenetic homologs SirR in Staphylococcus epidermidis and MntR in Staphylococcus aureus. Importantly, these metalloregulators function as transcription factors that modulate the expression of bacterial virulence genes and high affinity metal ion uptake systems related to virulence and oxidative stress. Work conducted in our laboratory on Streptococcus mutans, the principal acidogenic component of human dental plaque, revealed a DtxR homolog that regulates a repertoire of genes, and accumulating evidence is consistent with a role for iron in S. mutans biofilm formation, the oxidative stress response, and acid tolerance. Indeed, the identification and characterization of genes involved in these and other pathogenic processes is a high priority since they can prove to be future drug targets. The major goal of this research proposal will focus on elucidating iron-dependent gene regulation and its role in S. mutans-induced cariogenesis. The specific aims include 1) characterizing iron-responsive genes that belong to a putative S. mutans Dlg regulon; 2) cloning and characterizing other iron-dependent genes in S.mutans that are not subject to Dlg control; 3) examining the expression of S. mutans Dlg- and iron-responsive genes in environments that approximate the human oral cavity; and 4) establishing a correlation between Dlg/iron-regulated gene expression and S. mutans-induced cariogenesis. [unreadable] [unreadable]